Like this:

How small is small enough? Well, according to nanotechnology expects you can’t get small enough. Hmm … we wonder what their teenage years were like. ;)

From Science Daily:

Scientists from A*STAR’s Institute of Materials Research and Engineering (IMRE), led by Professor Christian Joachim,* have scored a breakthrough in nanotechnology by becoming the first in the world to invent a molecular gear of the size of 1.2nm whose rotation can be deliberately controlled. This achievement marks a radical shift in the scientific progress of molecular machines and is published on 14 June 20009 in Nature Materials.

Said Prof Joachim, “Making a gear the size of a few atoms is one thing, but being able to deliberately control its motions and actions is something else altogether. What we’ve done at IMRE is to create a truly complete working gear that will be the fundamental piece in creating more complex molecular machines that are no bigger than a grain of sand.”

Prof Joachim and his team discovered that the way to successfully control the rotation of a single-molecule gear is via the optimization of molecular design, molecular manipulation and surface atomic chemistry. This was a breakthrough because before the team’s discovery, motions of molecular rotors and gears were random and typically consisted of a mix of rotation and lateral displacement. The scientists at IMRE solved this scientific conundrum by proving that the rotation of the molecule-gear could be well-controlled by manipulating the electrical connection between the molecule and the tip of a Scanning Tunnelling Microscope while it was pinned on an atom axis.